Food, not the photoperiod, entrains the circadian rhythms in the liver of Winstar albino rats

The central oscillator is located in mammals' suprachiasmatic nucleus (SCN). The liver is the non-photic organ and the centre for metabolic activities. Food could be a potential zeitgeber for the liver as the timing of feeding is precise in animals. The present study hypothesized that the food provided at a different time of the day (consistently delay of 6 hours) could lead to the desynchronization of daily rhythms in clock genes in liver tissues.  The Winstar albino rats were divided into three groups and were exposed to a daily light-dark cycle (12L:12D; 12h light and 12h dark). The Group 1 (Control group) had food ad libitum, Group 2- second group- 6h food group had daily food availability of 6h (night fed group). In contrast, Group 3- T30 group was provided food for 6 hours but delayed by 6h from the previous day's food timing. After 30 days, animals were sacrificed at six-time points and the expression of clock genes was studied in the liver. Food cycle's effect was observed on body mass, and it was significantly (P < 0.05) reduced in the T30 group. The circadian clock persisted in both food ad libitum and night fed groups but changed in phase and amplitude. However, it lost daily rhythm in clock genes in liver tissues of the T30 group. These results are significant as they suggest that the food's timing is critical for synchronizing the circadian clock in the metabolic center, i.e., the liver